1.Field of the Invention
The present invention relates to the field of gas turbine engines and relates in particular to a turbojet engine having a front fan.
2.Description of the Related Art
The rotor of the turbofan of an engine fitted to civil airplanes comprises a disk driven by the low-pressure shaft. A plurality of blades extend radially from the periphery of the disk, and the blades are held by their end forming the root. In a common type of structure, the blade root has a dovetail cross section and the blades are housed in recesses machined into the rim of the disk in an axial direction. Located immediately downstream of the fan disk and forming the same rotor is the low-pressure compressor. The latter is in the form of a drum and comprises a number of blade stages. The fan disk is secured to the low-pressure compressor drum by being bolted to a radial flange of the latter. The flange is furthermore provided with notches forming a means for axial retention of the blades of the fan disk. Each blade root is provided downstream with an axial extension having two radial grooves and is inserted into a notch at the grooves such that it is locked in the axial direction.
In normal operation, the aerodynamic forces on the blades of the fan have an axial resultant directed upstream. However, when the engine is driven in autorotation, the forces on the blades are reversed. Despite the abovementioned axial locking, there is a clearance and a downstream movement occurs. The downstream transverse edge of the part of the blade forming the shank, between the dovetail root and the platform, then presses against the upstream flange of the low-pressure compressor drum. Wear has been observed on the upstream face of this flange, in the regions located in line with the recesses in the fan disk.
The problem associated with this wear phenomenon results from the presence, in these regions, of drill holes made to relieve the stresses in the flange. The blade that presses against the flange in a drilled region is itself eroded. The wear on the shank is thus not uniform. The surface of the downstream face of the shank is only worn to the extent that it comes into contact with the flange; the surface portion in line with the drill hole is not worn and eventually becomes prominent. This results in undesirable clearances developing between the blades and the flange.